This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
A subscriber identity module (SIM) is an integrated circuit that securely stores information to authenticate subscribers for carriers on mobile, wireless devices (such as mobile phones and computers). Such information can include, e.g., the International Mobile Subscriber Identity (IMSI).
Many mobile devices allow multiple SIM cards to be used. Such SIM cards could be, e.g., prepaid, pay as you use, or associated with a contract with an operator. Typically, each SIM card is associated with a single operator. This means for mobile devices allowing use of multiple SIM cards, for switching between SIM cards, operators are also switched. Switching operators entails a corresponding switch in phone numbers and IP (internet protocol) addresses for the mobile device, and may entail switching other connectivity information such as email addresses.
Because a switch in operators causes a corresponding switch in phone numbers to a new phone number, anyone trying to call the original phone number (before the switch in SIM cards) will not reach the new phone number, as the SIM card corresponding to that old phone number is no longer in use. Similarly, anyone trying to reach the mobile device using the original IP address of the mobile device (before the switch in SIM cards) will not be able to reach the mobile device, as the original IP address is no longer valid for the mobile device. Thus, certain P2P (peer-to-peer) applications will no longer function correctly.
It is also possible, for instance in the case of a software (SW) SIM or embedded SIM, that the SIM can allow for multiple operators to be served with the same SIM. That is, multiple IMSIs and perhaps corresponding phonebook numbers can be held in the same SIM. However, this does not change the problems described above, as anyone trying to reach a new phone number or mobile IP address caused by a change in operator for a single SIM allowing multiple operators to be selected still will not be able to reach the new phone number or IP address.
Thus, while allowing users to use multiple SIMs has benefits, switching between SIMs causes the problem that the users who switch between SIMs are no longer reliably reachable. This problem exists for every user using multiple SIM cards: How does one reliably reach someone who uses multiple SIMs?